According to the 3GPP standard, a subscriber can be intercepted based on Mobile Station International ISDN Number MSISDN, International Mobile Subscriber Identity IMSI and International Mobile Equipment Identity IMEI. The target identities for 3GPP MS CS and GPRS interception at the SGSN, GGSN, 3G MSC Server and 3G GMSC Server can be at least one of the following: IMSI, MSISDN or IMEI.
FIG. 1 is part of the prior art and discloses an Intercept Mediation and Delivery Unit IMDU, also called Intercept Unit. The IMDU is a solution for monitoring of Interception Related Information IRI and Content of Communication CC for a target. The different parts used for interception are disclosed in current Lawful Interception standards (see 3GPP TS 33.108 and 3GPP TS 33.107—Release 7). A Law Enforcement Monitoring Facility LEMF is connected to Mediation Functions MF, MF2 and MF3 respectively for ADMF, DF2, DF3 i.e. an Administration Function ADMF and two Delivery Functions DF2 and DF3. The Administration Function and the Delivery Functions are each one connected to the LEMF via standardized handover interfaces HI1-HI3, and connected via interfaces X1_1, X2, X3 to an Intercepting Control Element ICE in a telecommunication system. Together with the delivery functions, the ADMF is used to hide from ICEs that there might be multiple activations by different Law Enforcement Agencies. Messages REQ sent from LEMF to ADMF via HI1 and from the ADMF to the network via the X1_1 interface comprise identities of a target that is requested to be monitored. The Delivery Function DF2 receives Intercept Related Information IRI from the network via the X2 interface. DF2 is used to distribute the IRI to relevant Law Enforcement Agencies via the HI2 interface. Intercept Related Information IRI, received by DF2 is triggered by Events that in Circuit Switching domain are either call related or non-call related. In Packet Switching domain the events are session related or session unrelated. The Delivery Function DF3 receives Content of Communication CC, i.e. speech and data, on X3 from the ICE. In Circuit Switching, DF3 is responsible for call control signaling and bearer transport for an intercepted product. Keeping focus on the scope of this proposal, impacted areas are the ICE, the interfaces X1_1, X2 and X3 and consequently the interfaces HI1, HI2 and HI3.
Requests are also sent from the ADMF to a Mediation Function MF2 in the DF2 on an interface X1_2. The requests sent on X1_2 are used for activation of Intercept Related Information IRI, and to specify detailed handling options for intercepted IRI. For the activation of Intercept Related Information IRI the message sent from the ADMF to the DF2 contains:                The target identity;        The address for delivery of IRI (=LEMF address);        Which subset of information shall be delivered;        A DF2 activation identity which uniquely identifies the activation for DF2 and is used for further interrogation or deactivation, respectively;        The IA in case of location dependent interception;        The warrant reference number if required by national option.        
Intercept Related Information IRI events are necessary at the start and end of the call, for all supplementary services during a call and for information which is not call associated. There are call related events and non call related events. If an event for/from a mobile subscriber occurs, the ICE sends the relevant data to the DF2. A similar situation applies to the case of PS domain.
The Delivery Function DF3 receives Content of Communication CC, i.e. speech and data, on X3 from the ICE. Requests are also sent from the ADMF to a Mediation Function MF3 in the DF3 on an interface X1_3. The requests sent on X1_3 are used for activation of Content of Communication, and to specify detailed handling options for intercepted CC. In Circuit Switching, DF3 is responsible for call control signaling and bearer transport for an intercepted product.
The scenario for delivery of the Content of Communication CC is as follows. At call attempt initiation, for one 64 kbit/s bi-directional target call, two ISDN delivery calls are established from the DF3 to the LEMF. One call offers the Content of Communication CC towards the target identity (CC Rx call/channel), the other call offers the Content of Communication CC from the target identity (CC Tx call/channel). The above discussed scenario is called Stereo delivery. In case ‘call from’ and ‘call to’ monitored subscriber are mixed and delivered using one CC call/channel, it is called Mono delivery. The standard ETSI defines the following delivery types for Stereo delivery in case of multi party calls:                Stereo, Option A—Separate CC links for each call, active or not active. A network option allows switching to off or on the communication towards to the LEMF for the non-active call (i.e. to send or not the call contents of the held parties in multi party calls towards the LEMF).        Stereo, Option B—The CC links are only used for calls active in their communication phase (this option is also called “Reuse of CC links for active calls”).        
To assure correlation between the independently transmitted Content of Communication CC and Intercept Related Information IRI of an intercepted call the following parameters are used:                Lawful Interception IDentifier (LIID)        Communication IDentifier (CID)        CC Link IDentifier (CCLID)        
These parameters are transferred from the DF2 and DF3 to the LEMF over HI2 and HI3 respectively.
As a normal behavior, a target subscriber is intercepted by a same Law Enforcement Agency LEA (for example national police) by ordering monitoring on all the target identity types (MSISDN, IMSI and IMEI) that could belong to the target subscriber. A reason is that a certain identity could be not available in a specific traffic case and the assumption is that all traffic events have to be monitored and sent to LEA. In addition, the target multiple identities are usually set on the whole network; as a consequence, the monitoring events are notified to LEA several times depending on the presence of multiple ICEs in the traffic chain.
By considering the above, in case a subscriber is intercepted by the same LEA for both Call Data and Call Content on several target identities (MSISDN, IMSI and IMEI) and in case the Call Content delivery type is the same (Mono, Stereo Option A or Stereo Option B) for all the target identities:                the same set of IRI events are sent from ICE to DF2 for each target identity;        the same Content of Communication CC is sent from ICE to DF3 for each target identity.        
Furthermore duplication of IRI events and Call Content delivery is a major issue not only due to multiple activations on different identities in one ICE, but also due to the uncorrelated delivery from the multiple ICEs in traffic chain related to the same call/session. This multiple deliveries related to the same call/session (due to multiple monitored identities in single/multiple ICEs) causes that:                The ICEs are loaded to provide duplicated information, for both IRI and CC monitoring, of the same call related/call unrelated event (e.g. any call attempt is signaled from the multiple ICEs in the traffic chain per each monitored identity . . . );        Large amount of duplicated and useless data are delivered to the LEMF/Monitoring Centre;        A large amount of duplicated data could lead to congestion on both X2 and HI2 with possible consequence of capacity wasting for other possible monitoring instances;        For CS monitoring, the usage of many CC links for delivery the same communication of content could lead to missing monitoring in case of limited number of CC links;        The duplication of delivered CC is a critical aspect in Packet Switching PS domain, where the amount of delivered CC volumes is usually several order larger than delivered IRIs, even more in case of multiple deliveries of a same CC. The drawback is even worse in case of multiple deliveries to a Law Enforcement Agency from the mediation function in case of multiple ICEs in the traffic chain;        The LEMF/Monitoring Centre will get a large amount of duplicated information in term of IRI and Content of Communication that requires time and resources to analyze duplicated information.        